1. Field
The present invention relates to an optical scanning element for an optical scanner used in a laser printer or a projection-type display device. The present invention particularly relates to an optical scanning element which swings a reflection mirror by oscillating an oscillating body.
2. Description of the Related Art
Conventionally, there has been known an optical scanning element which forms a projection image by scanning laser beams which are modulated in response to image signals in a projection-type display device or the like. For example, a rotary multi-face mirror (polygon mirror) or an oscillation-drive-type reflection mirror (Galvano mirror) has been used. Out of these mirrors, the oscillation-drive-type reflection mirror can miniaturize a drive part compared to the rotary multi-face mirror and hence, the oscillation-drive-type reflection mirror is preferably applicable to a light-weighted and miniaturized optical scanning element.
FIG. 16 is an exploded perspective view showing a Galvano-mirror-type optical scanning element 100 described in JP-A-2003-57586 (patent document 1). An oscillating body 103 is mounted on a base frame 101 by way of support portions 102 which are formed on both sides of the base frame 101. The oscillating body 103 is a unitary body constituted of a reflection mirror portion 105, a fixed frame 104 which is formed around the reflection mirror portion 105, and torsional spring portions 106 which connect the reflection mirror portion 105 and the fixed frame 104 and support the reflection mirror portion 105 from both sides. The torsional spring portions 106 are formed along an axis which passes the center of gravity of the reflection mirror portion 105, and constitute rotary shafts for the torsional rotation of the reflection mirror portion 105.
A pair of fixed electrodes 107, 108 is mounted on the base frame 101 at positions where the fixed electrodes 107, 108 face the reflection mirror portion 105 in an opposed manner. A voltage is applied between the oscillating body 103 and the pair of fixed electrodes 107, 108. Here, the voltage is alternately applied using a changeover switch SW. Due to such an application of the voltage, an electrostatic force acts between the fixed electrodes 107, 108 and the reflection mirror portion 105 so as to allow the fixed electrodes 107, 108 and the reflection mirror portion 105 to attract each other. By alternately applying the voltage to the pair of fixed electrodes 107, 108, the reflection mirror portion 105 is swung using the torsional spring portions 106 as a rotation axis.
FIG. 17 is a conceptual view of a projection-type display device in which the optical scanning element 100 scans a reflection optical flux 112 formed by reflection of an incident light, and projects the reflection optical flux 112 on a screen 113. The optical flux 111 radiated from a light source 110 with image modulation is radiated to the reflection mirror portion 105 of the optical scanning element 100. Since the reflection mirror portion 105 is swung, the reflection optical flux 112 oscillates vertically thus drawing a vertical trajectory on the screen 113. For example, in a state that the image modulated optical flux 111 from the light source 110 is subject to horizontal scanning in synchronism with a horizontal scanning period of image data contained in the optical flux 111, by swinging the reflection mirror portion 105 in synchronism with the vertical scanning period of the above-mentioned image, an image can be displayed on the screen 113.